The invention relates to a turbine system for recovering energy of exhaust gases of an internal combustion engine. More particularly the present invention relates to improvements of such turbine systems.
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other applications utilizing turbine systems such as aero or marine systems.
Vehicles may be provided with turbine systems for recovering energy of the exhaust gas flow from an internal combustion engine. A turbine system may e.g. include a turbocharger which purpose is to convert the energy of the exhaust gas into a pressure increase of the intake air to the internal combustion engine, and a turbocompound unit which purpose is to convert the remaining energy into a rotational movement of a shaft. The rotational movement of the shaft is transferred as a torque increase to the crankshaft of the engine of the vehicle. Other known turbine systems include two turbochargers arranged in series such that the intake air is compressed in two stages, an initial compression by means of one of the turbochargers, and a final compression by means of the second turbocharger.
The use of turbine systems has proven to provide significant advantages on driving economics as well as on the environment; the energy recovery from the exhaust gas flow will in fact reduce the fuel consumption of the vehicle.
U.S. Pat. No. 5,119,633 describes an internal combustion engine and a turbine system having a turbocharger arranged in series with a downstream turbocompound device. A bypass channel is provided which can be opened or closed by means of a moveable shroud; in a closed position all of the exhaust gas flows through the turbocompound unit, while in an open position most of the exhaust gas bypasses the turbocompound unit.
The turbocompound device of the above-described system will produce a torque increase to the crankshaft which is not always desirable. Furthermore it is not possible to restrict the flow of exhaust gas through the turbine for engine braking. Therefore, there is a need for an improved turbine system.
It is desirable to provide a turbine system/method, which creates conditions for an improved efficiency, at least in some operational conditions.
By the provision of a flow control valve for bypassing exhaust gases passed the second turbine device and a pneumatic valve between the first and second turbine devices, it is possible to shut off the flow to the second turbine device substantially, whereby back pressure may be accurately controlled by regulating the flow control valve of the bypass channel.
Preferably the pneumatic valve is an on/off valve. This is advantageous in that the pneumatic valve is operated in a robust manner since the pneumatic valve, when otherwise controlled variable thus allowing for intermediate positions between an open position and a closed position, may give rise to oscillations.
The turbine system may comprise a controller being connected to the flow control valve and to the on/off valve for regulating the valves. Back pressure and bypass amount is thereby controlled in a very efficient manner.
The controller may in some embodiments be configured to regulate the on/off valve in either a fully open position or in a closed position, thus reducing the risk for oscillations effectively.
The on/off valve may be an exhaust gas pressure regulator forming part of a diffuser for the exhaust gas flowing through the turbine system. The on/off valve is thereby implemented as an existing component in the exhaust gas flow path whereby the additional space required for such construction is greatly reduced.
The flow control valve is preferably continuously variable between two end positions. When the on/off valve is closed it is thereby possible to accurately control the back pressure, as well as the bypass amount, according to desired operating parameters.
The flow control valve may comprise a moving member which in a first end position is closing a bypass channel formed by said moving member, and which in a second end position is opening said bypass channel. The moving member may further be configured to move in a linear direction. The moving member may form part of a sliding wall, and the sliding wall may surround the on/off valve such that the bypass channel forms an annular channel radially outside the on/off valve. The flow control valve may consequently be provided in a robust manner, whereby the annular symmetric shape allows for efficient packaging and good aerodynamics.
The bypass channel may extend from an outlet of the first turbine device to an outlet of the second turbine device such that no or very little amount of exhaust gas will be allowed to enter the inlet of the second turbine device when the on/off valve is closed.
The turbine system may further comprise a bypass pipe, and the flow control valve may be arranged inside the bypass pipe for regulating the flow through the bypass pipe. The bypass pipe may extend from an outlet of the first turbine device to an outlet of the second turbine device. The bypass pipe may thus extend outside an exhaust gas flow path connecting the first and second turbine devices, which is advantageous in that very little modifications need to be made of existing turbine devices.
The first turbine device may be a turbocharger device, and the second turbine device may be a turbocharger device or a turbocompound device arranged in series with the first turbine device.
According to another aspect, a vehicle comprising a turbine system according to the first aspect is provided.
A method for controlling a turbine system configured to recover energy of exhaust gases of an internal combustion engine is also provided. The turbine system comprises a first turbine device, a second turbine device, a flow control valve for bypassing the second turbine device, and a pneumatic valve arranged between the first turbine device and the second turbine device. The method further comprises the steps of determining if the pneumatic valve should be in a fully open position or in a closed position resulting in a desired position of the pneumatic valve, controlling the position of the pneumatic valve in accordance with its desired position, determining if the flow control valve should be in a fully open position, a semi-open position, or in a closed position resulting in a desired position of the flow control valve, and controlling the position of the flow control valve in accordance with its desired position.
The step of controlling the position of the pneumatic valve according to a fully open position may comprise arranging the pneumatic valve in an end position, and the step of controlling the position of the pneumatic valve according to a closed position may comprise arranging the pneumatic valve in an opposite end position.
According to a further aspect, a computer program is provided comprising program code means for performing the steps of the above-mentioned method when said program is run on a computer.
According to a yet further aspect a computer readable medium carrying a computer program is provided comprising program code means for performing the steps of the above-mentioned method when said program product is run on a computer.
A control unit is also provided for controlling the operation of a turbine system, the control unit being configured to perform the steps of the above-mentioned method.